xxHash - Extremely fast hash algorithm ====================================== xxHash is an Extremely fast Hash algorithm, running at RAM speed limits. It successfully completes the [SMHasher](http://code.google.com/p/smhasher/wiki/SMHasher) test suite which evaluates collision, dispersion and randomness qualities of hash functions. Code is highly portable, and hashes are identical on all platforms (little / big endian). |Branch |Status | |------------|---------| |master | [](https://travis-ci.org/Cyan4973/xxHash?branch=master) | |dev | [](https://travis-ci.org/Cyan4973/xxHash?branch=dev) | Benchmarks ------------------------- The benchmark uses SMHasher speed test, compiled with Visual 2010 on a Windows Seven 32-bit box. The reference system uses a Core 2 Duo @3GHz | Name | Speed | Quality | Author | |---------------|----------|:-------:|------------------| | [xxHash] | 5.4 GB/s | 10 | Y.C. | | MurmurHash 3a | 2.7 GB/s | 10 | Austin Appleby | | SBox | 1.4 GB/s | 9 | Bret Mulvey | | Lookup3 | 1.2 GB/s | 9 | Bob Jenkins | | CityHash64 | 1.05 GB/s| 10 | Pike & Alakuijala| | FNV | 0.55 GB/s| 5 | Fowler, Noll, Vo | | CRC32 | 0.43 GB/s| 9 | | | MD5-32 | 0.33 GB/s| 10 | Ronald L.Rivest | | SHA1-32 | 0.28 GB/s| 10 | | [xxHash]: http://www.xxhash.com Q.Score is a measure of quality of the hash function. It depends on successfully passing SMHasher test set. 10 is a perfect score. Algorithms with a score < 5 are not listed on this table. A more recent version, XXH64, has been created thanks to [Mathias Westerdahl](https://github.com/JCash), which offers superior speed and dispersion for 64-bit systems. Note however that 32-bit applications will still run faster using the 32-bit version. SMHasher speed test, compiled using GCC 4.8.2, on Linux Mint 64-bit. The reference system uses a Core i5-3340M @2.7GHz | Version | Speed on 64-bit | Speed on 32-bit | |------------|------------------|------------------| | XXH64 | 13.8 GB/s | 1.9 GB/s | | XXH32 | 6.8 GB/s | 6.0 GB/s | This project also includes a command line utility, named `xxhsum`, offering similar features as `md5sum`, thanks to [Takayuki Matsuoka](https://github.com/t-mat) contributions. ### License The library files `xxhash.c` and `xxhash.h` are BSD licensed. The utility `xxhsum` is GPL licensed. ### Build modifiers The following macros can be set at compilation time, they modify xxhash behavior. They are all disabled by default. - `XXH_INLINE_ALL` : Make all functions `inline`, with bodies directly included within `xxhash.h`. There is no need for an `xxhash.o` module in this case. Inlining functions is generally beneficial for speed on small keys. It's especially effective when key length is a compile time constant, with observed performance improvement in the +200% range . See [this article](https://fastcompression.blogspot.com/2018/03/xxhash-for-small-keys-impressive-power.html) for details. - `XXH_ACCEPT_NULL_INPUT_POINTER` : if set to `1`, when input is a null-pointer, xxhash result is the same as a zero-length key (instead of a dereference segfault). - `XXH_FORCE_MEMORY_ACCESS` : default method `0` uses a portable `memcpy()` notation. Method `1` uses a gcc-specific `packed` attribute, which can provide better performance for some targets. Method `2` forces unaligned reads, which is not standard compliant, but might sometimes be the only way to extract better performance. - `XXH_CPU_LITTLE_ENDIAN` : by default, endianess is determined at compile time. It's possible to skip auto-detection and force format to little-endian, by setting this macro to 1. Setting it to 0 forces big-endian. - `XXH_FORCE_NATIVE_FORMAT` : on big-endian systems : use native number representation. Breaks consistency with little-endian results. - `XXH_PRIVATE_API` : same impact as `XXH_INLINE_ALL`. Name underlines that symbols will not be published on library public interface. - `XXH_NAMESPACE` : prefix all symbols with the value of `XXH_NAMESPACE`. Useful to evade symbol naming collisions, in case of multiple inclusions of xxHash source code. Client applications can still use regular function name, symbols are automatically translated through `xxhash.h`. - `XXH_STATIC_LINKING_ONLY` : gives access to state declaration for static allocation. Incompatible with dynamic linking, due to risks of ABI changes. - `XXH_NO_LONG_LONG` : removes support for XXH64, for targets without 64-bit support. ### Example Calling xxhash 64-bit variant from a C program : ```c #include "xxhash.h" unsigned long long calcul_hash(const void* buffer, size_t length) { unsigned long long const seed = 0; /* or any other value */ unsigned long long const hash = XXH64(buffer, length, seed); return hash; } ``` Using streaming variant is more involved, but makes it possible to provide data in multiple rounds : ```c #include "stdlib.h" /* abort() */ #include "xxhash.h" unsigned long long calcul_hash_streaming(someCustomType handler) { XXH64_state_t* const state = XXH64_createState(); if (state==NULL) abort(); size_t const bufferSize = SOME_VALUE; void* const buffer = malloc(bufferSize); if (buffer==NULL) abort(); unsigned long long const seed = 0; /* or any other value */ XXH_errorcode const resetResult = XXH64_reset(state, seed); if (resetResult == XXH_ERROR) abort(); (...) while ( /* any condition */ ) { size_t const length = get_more_data(buffer, bufferSize, handler); /* undescribed */ XXH_errorcode const addResult = XXH64_update(state, buffer, length); if (addResult == XXH_ERROR) abort(); (...) } (...) unsigned long long const hash = XXH64_digest(state); free(buffer); XXH64_freeState(state); return hash; } ``` ### Other programming languages Beyond the C reference version, xxHash is also available on many programming languages, thanks to great contributors. They are [listed here](http://www.xxhash.com/#other-languages). ### Branch Policy > - The "master" branch is considered stable, at all times. > - The "dev" branch is the one where all contributions must be merged before being promoted to master. > + If you plan to propose a patch, please commit into the "dev" branch, or its own feature branch. Direct commit to "master" are not permitted.